1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to semiconductor processing fluid delivery systems and to method of delivering semiconductor processing fluids.
2. Description of the Related Art
Conventional chemical mechanical planarization (“CMP”) processes involve the planarization of a surface of a wafer or workpiece through the use of an abrasive slurry and various rinses and solvents. Material removal from the workpiece surface is through a combination of abrasive action and chemical reaction. In many processes, a quantity of abrasive slurry is introduced onto a polish pad or platen of the CMP tool and distributed across the surface thereof by means of centrifugal force. Thereafter, one or more wafers are brought into sliding contact with the polish pad for a select period of time.
In many conventional CMP systems, processing fluids such as slurries, solvents and rinses are dispensed from a static dispense tube that is centrally positioned above the polish pad. The polish pad is fitted with an upwardly projecting dispersal cone that is designed to disperse processing fluid dispensed from above laterally across the polishing surface of the polish pad. The action of the fluid flowing down the sloped surfaces of the dispersal cone along with centrifugal force associated with the rotation of the polish pad is intended to provide a fairly uniform layer of processing fluid across the surface of the polish pad.
A more recent innovation involves the use of so-called high selectivity slurry. Conventional high selectivity slurry mixtures contain a slurry additive that functions in the conventional sense. However, a slurry additive is mixed with the slurry to provide a selectivity of polish of an overlying film relative to an underlying film. A common application involves CMP of an overlying silicon dioxide film selectively to an underlying silicon nitride film. The slurry additive slows the chemical activity of the slurry when the polish exposes the underlying silicon nitride. It is desirable, though not currently possible, to maintain precise control over the flow rates of the slurry and the slurry additive. Deviations in the flow rate of either component can lead to poor selectivity and film non-uniformity.
One conventional means of delivering CMP slurry to a platen involves the use of peristaltic pumps. A peristaltic pump, as the name implies, utilizes peristaltic or squeezing action to squeeze a pliable container, usually a plastic tube, in order to pump the working fluid. One difficulty associated with the peristaltic pumping is a propensity for the pump's actual flow rate to deviate significantly from the desired flow rate. The reasons for such deviations are legion, and include variations in the elasticity of the compliant tubing, non-uniformity in the composition of the slurry, and air trapped in the line to name just a few.
The delivery of high selectivity slurry introduces another set of complexities. As noted above, the ratio of flow rates of the slurry and the slurry additive in a high selectivity slurry context should be carefully controlled in order to achieve the desired selectivity of CMP activity. However, if peristaltic pumping is used for both the slurry additive and the slurry, then deviations can arise in the flow ratios and thus non-uniformity in CMP processing may result.
Various conventional retrofit designs for high selectivity slurry delivery have been developed. These conventional retro fit systems are generally designed to retrofit into an existing CMP tool and take over some of the functionality of working fluid delivery to the platen. A disadvantage associated with these conventional high selectivity slurry retrofit systems is sometimes poor control of the flow rates of each of the constituents, that is, the slurry and the slurry additive, and an inability to provide a mixing of the slurry and the slurry additive prior to delivery to the platen.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.